This invention relates to hand-held laser devices and, in particular, to a compact, effective heat sink for a high power, hand held laser.
A laser diode is a relatively efficient light emitter, converting fifty to sixty percent of applied power into light, the remainder being dissipated as heat. High power, semiconductor lasers are particularly susceptible to damage because the heat is generated in a small volume at a high rate. Because of this, laser diodes are typically mounted with the active surface of the die, i.e. the surface containing the laser diode, mounted face down on a heat sink to minimize the thermal path from the diode to the heat sink. As used herein, xe2x80x9claser diodexe2x80x9d refers to a semiconductor device having one or more laser diodes on a single die, typically as parallel stripes, and operated together as a set. In other words, the use of the singular does not exclude the plural in reference to a laser diode.
A heat sink of the prior art includes a mass of metal, typically copper, attached to the packaged semiconductor laser device. Thus, heat flows from the diode junction, through several interface layers, through the metal tab of the semiconductor package to the heat sink. The heat sink typically extends away from the semiconductor device and the heat flows essentially in one direction away from the junction.
There are several interfaces in the thermal path away from the laser diode to a heat sink and an intimate contact must be maintained between adjoining surfaces to assure a low thermal resistance across the interfaces. Within the semiconductor device, compatible metal layers, e.g. nickel, gold, and other metals, are deposited in a clean room environment to assure a good thermal and mechanical bond between the layers. The bond between the semiconductor device and a heat sink is typically aided by thermally conductive grease that helps xe2x80x9cwetxe2x80x9d the two surfaces to assure a large contact area even if the surfaces are macroscopically rough, e.g. a matte finish rather than a high polish.
U.S. Pat. No. 5,561,684 (Martin) discloses a diode laser pump source in which a laser diode is soldered to a heat sink and the heat sink is mounted on a flat portion of a base having a semicircular cross-section. The base fits within a cylindrical casing that radiates and dissipates heat in a 360xc2x0 pattern and acts as another heatsink for the laser diode.
U.S. Pat. No. 5,550,853 (Ostler) discloses a compact gas discharge laser having a heat sink that circumferentially surrounds the laser and includes an external blower provides axial cooling through a port in the housing containing the laser.
Even a laser diode properly mounted on a heat sink often must be operated intermittently to give the laser diode a chance to cool between operations. An alternative is a larger heat sink or a lower power laser, neither of which may be feasible in many applications. For example, many areas of medicine have developed uses for lasers in the treatment of patients, such as a blue laser for the treatment of skin disorders by dermatologist. In such applications, a hand held device, even if coupled to a power source by a cable, is preferable to an appliance that must be maneuvered about a patient. Thus, simply providing a large heat sink is not feasible.
A hand held device puts severe restrictions on the size of a heat sink. A laser that is adequately cooled is not of much use if a physician cannot comfortably hold and manipulate the device. Further, a human hand is both a source of heat and sensitive to temperature, factors which must be considered in designing a heat sink for a hand held product.
In view of the foregoing, it is therefore an object of the invention to provide a heat sink for a high power laser diode, i.e. a laser diode dissipating a total power of one to sixty watts or more.
Another object of the invention is to provide a heat sink for a laser diode wherein the heat sink spreads heat in many directions away from the laser diode.
A further object of the invention is to provide a heat sink for a laser diode wherein the heat sink provides a low resistance path for heat to flow away from the laser diode.
Another object of the invention is to provide a heat sink for a laser diode wherein the heat sink provides a convenient hand grip.
A further object of the invention is to provide a heat sink that removes heat from five sides of a semiconductor laser.
The foregoing objects are achieved in this invention in which a laser diode is mounted on a plate that fits closely within a mortise in a thermally conductive insert. The insert fits closely within a thermally conductive sleeve. The plate has six sides and the laser diode is attached to one of the sides. Heat is removed from the remaining five sides of the plate. The insert includes a conic section that fits within a conic section in the sleeve to provide good thermal contact between the insert and the sleeve. The sleeve includes a plurality of holes and contains a fan for circulating air through the sleeve, thereby removing heat from the sleeve. The sleeve has a cylindrical portion for being held in a hand.